1. Field of the Invention
The present invention relates to a control apparatus of a hybrid vehicle which is driven by an engine and an electric motor, in particular, to one for controlling the amount of assisted (or auxiliary) output by the motor which assists the engine output when the vehicle is driven at high speed.
2. Description of the Related Art
Conventionally, a hybrid vehicle having not only the engine but also an electric motor as the drive source is known.
As a hybrid vehicle, a parallel hybrid vehicle is known, which uses an electric motor as an auxiliary drive source for assisting the engine output. In the parallel hybrid vehicle, the engine output is assisted using the electric motor during the accelerating operation (i.e., acceleration mode), while during the decelerating operation (i.e., deceleration mode), the battery and the like are charged via a regenerating operation, that is, "deceleration regeneration" is performed. According to various control operations including the above, the remaining capacity (corresponding to the electric energy) of the battery is maintained while the driver's demands can also be satisfied. An example thereof is disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 7-123509.
According to the control apparatus of such conventional hybrid vehicles, for example, in the acceleration mode, an assist driving force using a motor is also output in addition to the driving force obtained by the engine output. This output assist by the motor for assisting the engine output is continuously performed even in the high-speed driving mode in which the fuel supply to the engine is cut off according to a specific limit defined by the fuel supply. In this case, the engine side controls the vehicle so as to decrease its speed, but the motor side still controls the vehicle so as to assist the driving force obtained by the engine output. Therefore, these controls are inconsistent with each other.
Due to such an unnecessary assist by the motor, the battery capacity may be decreased, thereby causing excessive discharge of the battery.